The present invention is directed to three dimensional back projection method and an X-ray CT (computed tomography) apparatus, more specifically to three dimensional back projection method and an X-ray CT apparatus allowing the computation to be decreased by the image reconstruction based on the projection data obtained by the axial scan or helical scan using a multidetector (referred to as “cone beam reconstruction”).
Current mainstream X-ray CT apparatuses uses filtered back projection scheme for reconstruction of a CT image through data capturing, preprocessing, filtering, back projecting and postprocessing.
In the filtering, FFT operation is performed on the raw data, which is then multiplied by a reconstruction function in a frequency domain and thereafter reverse FFT operation is performed thereon.
Related Prior Art is disclosed in Japanese Published Unexamined Patent Application No. S59-168840.
Recently, X-ray CT apparatuses using a multidetector having a number of detector arrays are being developed.
The raw data obtained by using such a multidetector may have a huge data size, causing a problem that the FFT operation in the filtering may become huge. For example, in case of a multidetector having 256 detector arrays, there is a problem that at least 256 FFT operations are needed for every view.